-: (Instructor) So a quick lecture
to understand rules as a whole.
So rules are set up on your application load balancer
and you can have many rules or one rule too,
and the last rule is called the default rule
and each rule will have a specific target. Okay?
Now, the rules are going to be processed in order. Okay?
The default rule is going to be the last one to be processed
and each rule supports different actions.
For example, it can forward to a specific target group,
it can redirect to a specific other URL,
or it can send a fixed response back.
Rules can have conditions in terms of which rule is
going to be hit first.
So, it could be having a rule on the host header. Okay?
This is part of the client request.
It could be an HTTP request method to see if the request is
a GET or a POST, or a PUT.
The path pattern, so where the request is sent to,
is it slash my app 1 or slash my app 2.
Source IP, so what, where's the request coming from.
And a specific HTTP header in general,
or the query string parameters as part of the request.
So this really allows you to create some complex routing to
different target groups based on certain conditions
on the originating request.
Another thing you should know is that for a single rule,
as part of your ALB, you could have
multiple target groups as a target.
And the idea is that you can specify weights for each
target group within a single rule.
So the idea behind this is that you want to be able to
evolve your backend services, okay,
from one target group to another, and to update them.
And so you want to have version one in one target group
and version two in another target group.
And you want to evaluate whether or not
version two make sense.
This is also called a blue green deployment.
So thanks to this weighting,
you can control how much traffic goes from your ALB to
a specific target group as part of a rule.
So let's have a look at an example.
So let's say that we have our users,
they talked to the ALB and the ALB has been wired to talk to
target group one historically. Okay.
Which is your blue group,
but now you're going to add a target group two,
which is a new version of your application.
And you will set up weights in your rule.
You have a weight of eight, for target group one
and a weight of two for target group two.
That means that now for a single rule,
the ALB will send 80% of the traffic to your first group and
20% of the traffic to the second group,
which would allow you to do some monitoring on your target
groups and to see whether or not they are receiving the
traffic correctly,
whether or not the metrics are good, and whether or not your
application version is behaving as expected. Okay?
So this is a cool new feature as well.
So that's it for this lecture.
I hope you liked it.
And I will see you in the next lecture.